The present invention relates to a process for the production of cast iron containing spheroidal graphite. In this process, iron melt is treated with metallic magnesium to form the cast iron containing spheroidal graphite.
In the production of cast iron containg spheroidal graphite according to the process known as the converter process, a slag is formed which contains on the order of 5% by weight sulphur in the form of magnesium sulphide (MgS). At the usual treatment temperatures of between 1450 and 1550.degree. C., atmospheric oxygen can oxidize the magnesium sulphide. Thus, magnesium oxide is formed and the free sulphur strays back into the melt to form once again magnesium sulphide with the magnesium metal already dissolved therein. This process is called resulphurization and can, in extreme cases, lead to degeneration of the spherolites of graphite.
The methods used until know for overcoming the problem of resulphurization are unsatisfactory.
In a conventional process for producing cast iron, a slag dam is erected to hold back the slag. However, the slag dam only partially holds back the slag when the melt is being emptied from the converter into a transport vessel. This method requires a very costly cleaning of the converter.
In another known process, the iron melt is emptied together with the slag into a transport vessel. The de-slagging of the melt does not take place until they are in the transport vessel. The particular disadvantage of this process consists in the fact that during this process, resulphurization can still take place and is further encouraged by recasting. In addition, the deslagged melt cools down very quickly and casting of the melt has to take place without delay.
It is an object of the present invention to provide a process for producing cast iron containing spherical graphite wherein a stabilizing effect on the sulphur content in the converter slag is achieved so as to reduce or suppress resulphurization.